1. Field of the Invention
The subject invention relates to television receivers, and, more particularly, to the supply of operating power to a microprocessor controlling the functions in the television receiver.
2. Description of the Related Art
Most consumer electronic products, including television receivers, use a microprocessor to perform many of the needed functions of the product. This microprocessor needs to know when power is applied and also when power is removed in order to turn on and off in a safe and controlled manner. For example, if you turn off the television receiver when it was tuned to a specific channel and at specific settings of the volume, brightness, contrast, etc., when you turn the television receiver back on, it is desirable that the previous specific channel and settings are retained. This would be done by the microprocessor storing the various settings in memory. In order for the microprocessor to know that it needs to store these settings, it must receive a power OFF signal. Similarly, in order for the microprocessor to know that these settings need to be restored, it needs a power ON signal. The power ON signal informs the microprocessor that its operating power has been applied and is at the correct level for proper operation. The power OFF signal informs the microprocessor that its operating power will soon drop below its correct level for proper operation.
The power OFF signal must inform the microprocessor sufficiently early so that the microprocessor has sufficient time to perform all of its needed functions before the operating power drops from 5 VDC to 4.5 VDC. This small voltage difference along with the amount of time needed to perform the shutdown functions makes it difficult and impractical to use the V.sub.CC supply to sense the shutdown.